Simplied SequentialChain in LangChain

seuqential_chain.py

from langchain.chains import SequentialChain
from langchain.prompts import ChatPromptTemplate
from langchain.chains import LLMChain
from langchain.chat_models import ChatOpenAI

llm = ChatOpenAI(temperature=0.9)

class MyChain:
    def __init__(self, llm=None, template_engine=None):
        self.llm = llm
        self.chains = []
        self.outputs = []
        self.inputs = None
        self.template_engine= template_engine
    
    def first(self, prompt_txt: str, output: str):
        if len(self.chains) != 0:
            raise Exception("Chain is not empty")
            
        prompt = self.template_engine.from_template(prompt_txt)
        
        self.inputs = prompt.messages[0].prompt.input_variables
        self.next(prompt_txt, output)
        
    def next(self, prompt_txt: str, output: str):        
        prompt = self.template_engine.from_template(prompt_txt)
        self.outputs.append(output)
        chain = LLMChain(llm=llm, prompt=prompt, 
                     output_key=output
                    )
        self.chains.append(chain)

    def query(self, **inputs):
        overall_chain = SequentialChain(
            chains=self.chains,
            input_variables=self.inputs,
            output_variables=self.outputs,
            verbose=True
        )
        return overall_chain(inputs)
    
chain = MyChain(llm=llm, template_engine=ChatPromptTemplate)
chain.first("""
Translate the following review to {input_language}:

{Review}
""", "English_Review")
chain.next("""
Can you summarize the following review in 1 sentence:

{English_Review}
""", "summary") 
chain.next("""
What language is the following review:

{Review}
""", "language")
chain.next("""
Write a follow up response to the following summary in the specified language:

Summary: {summary}
Language: {language}
""", "followup_message")
print(chain.inputs)
chain.query(input_language="Chinese", Review="What is it?")